Catalytic cracking process



April 16,1946. 13.5.` GREENSFELDER ETAL 2,398,739

CATALYTIC CRACKING' PROCESS Filed April 6, 1945 52pm-afar ReqznczmforRagznarfor Reader inventors: Esas-nerd rangsfaldar 'ianlms ZmPerrgPatented Apr. 16,1946- l UNITED CATVALYTIC CRACKING PROCESS Bernard S.Greensfelder, Oakland, and Stanley Z. Perry, Berkeley, Calif., assignorsto Shell Development Company, San Francisco, Calif., a corporation ofDelaware Application April 6, 1945, Serial No. 586,925

(Cl. ISG-52) Claims.

This invention relates to an improved method for the production ofvaluable gaseous and normally'liquid hydrocarbon products from varioushydrocarbon oils by means of catalytic cracking.

An object of th'e invention is to provide a process for the 'catalyticcracking of various hydrocarbon` oils which aords particularly excellentyields of valuableolefins. Another object cf the invention is to providesuch a process wherein hydrocarbon oils may be converted into valuableliquid and gaseous products with a minimum formation of coke, carbon andsimilar undesired products. Still another object of the invention is toprovide a process for the catalytic cracking of hydrocarbon oils whichmay be carried out in small reactors with large production capacity.

In copending application, Serial Number 545,- 402, filed July- 17, 1944,of which the present application is a continuation-impart, there isdescribed an improved cracking process in which the catalytic crackingis carried out at a temperature above 1000 F. and preferably betwen 1200F. and 1400F. with a powdered solid adsorptive cracking catalyst dilutedwith such anamount of a substantially non-catalytic, non-adsorptive andnon-combustible mineral diluent that the depth of cracking is maintainedbelow yabout '70% and/or that no cooling is required in the regenerationof the catalyst. The present application is a continuation-impart ofsaidcopending application. y

The process of the invention is restricted to the catalytic conversionof hydrocarbon oils with solid catalysts in which the catalyst isrecycled in the formv of a powder through a zone wherein the conversionis effected under certain specined g iluid catalyst" system wherein thecatalyst is employedinfthe so-called "iluidized or pseudoin most allofthese various systems. It maybe very advantageously carried out in a"fluid catalyst system, and most advantageously carried out in thesomewhat modiiled fluid catalyst system hereinafter described. Since theinvention' is particularly advantageous for catalytic cracking in fluidcatalyst systems, the particulars of the invention will be described inconnection with such systems. It will be understood, however, that theinvention is not limited to this particular application. l t

In catalytic cracking in the above-mentioned types of systems there areat present two more or less distinct types of operation known as lowtemperature cracking" and high temperature cracking, respectively. Lowltemperature catalytic cracking refers to the more usual operationcarried out `at temperatures below about 900 F., usually between about700 F. and 850 F. High temperature catalytic cracking refers to the operation at temperatures above about 900 F., usually about 925 F. Hightemperature catalytic cracking has been carried out at temperaturesapproaching 1000 F. in at least two instances and this is considered tobe the upper temperature limit of such operations. It is possible tooperate at even higher temperatures, but such operation when carried outin the conventional manners give vastly inferior results as determinedby yields, product quality, amount of carbon or coke formed, 'catalystlife, and cost of operation. No

` practical or advantageous method of utilizing such temperatures isavailable and consequently such operation is'beyond the realm ofapplication.

According to the process of the invention hydrocarbon oils arecatalytically cracked atV temperatures above 550 C. or 1022 F., andpreferably between 1200 F. and 1400 F., under'such conditions and insuch a manner that improved,

f geous subclass of such systems is theso-called'i liquid state. Atypical fluid catalyst system is described in Ind. Eng, Chem. 35,768-773 (1943) The process ofthe invention may be carried out ratherthan inferior-results are obtained. According to the process of theinvention not only is the catalytic cracking carried out at temperaturesbeyond those considered useful in the conventional so-called hightemperature catalytic cracking process, but the regeneration of thecatalyst is also carried .out at temperatures above those generallyconsidered applicable. The regeneration temperature in the process ofthe invention is at least 50 C. (90 F.) above the reaction temperatureand therefore above 600 C.

(l112 FJ. Preferred temperatures are between about 1200 F. and 1500 FMany voi the most commonly used catalysts are not capable of withistanding regeneration by the conventional methods at temperatures muchabove 1100 F. without 5 l catalyst.

In the catalytic cracking of hydrocarbon oils the catalyst becomesdeactivated relatively rapidly due to the deposition of carbonaceouscokelike deposits. In order to operate continuously the catalyst iscontinuously recycled through a separate regeneration zone wherein thesecarbonaceous deposits are removed by burning, The burning of thecarbonaceous deposits liberates a large amount of heat and the amount ofheat liberated is more or less proportional to the amount of coke orcarbonaceous material deposited in the cracking step, In a typicalcommercial fluid catalyst cracking plant, for instance, about13,000`-l6,000 pounds of coke are burned perl hour. It is at presentconsidered necessary to retain the temperature of the catalyst in theregeneration at about 1100 F. or below. A portion of the heat ofcombustion is taken up in heating the regeneration gases and in raisingthe temperature of the catalyst. By far the major amount of the heat ofcombustion is removed by the use of suitable coils, or more generally byrecycling a portion of the catalyst undergoing regeneration through anexternal cooling device.` This cooling (extraction of heat) during theregeneration is difficult to effect evenly and eiciently and is.furthermore, wasteful. In the process of the invention the amount ofcooling required in the regeneration is very much less and in apreferred embodiment of the invention no cooling at all is necessary.

If it is attempted to operate the catalytic cracking process at thesehigh temperatures with the conventional catalysts in the otherwiseconventional manners it is found that the results'obtained (except thedepth 'of cracking) are much inferior to those obtained using theconventional high temperature cracking process in which the cracking iscarried out at temperatures from 'about 900 F. up to about 1000 F.Although the depth of cracking is materially increased the yield ofvaluable hydrocarbon gases such as the butylenes and propylene'are lowand the gasoline produced is of poor quality. Also it is found that thelosses to coke and carbon, and consequently the amount of coolingrequired to maintain the regeneration temperature, are much increased.

Thus, it is found that as the conversion per pass is increased,particularly in the region of (i5-'70% conversion, the rate of carbon orcoke deposition increases rapidly, (Depth of cracking is dened as 100-minus the percent by weight of the original feed recovered as an oilboiling above This is illustrated in the following table: Y v

Tinta Carbon formed in cracking second cut straight 4 Per cent Depth ofcracking cubo Thus by increasing the depth of cracking from to r70% (8%increase) the rate of carbon formation is increased 26%.

Contrary to expectation, however, it is found that for a given depth ofcracking the rate of carbon formation decreases as the temperature ofthe catalytic cracking is increased. Thus, by limiting the depth ofcracking according to the process of the invention the yield of coke orother carbonaceous deposits (calculated as carbon) may be considerablydecreased.

Also it is found, contrary to expectation, that unlike the yields ofhydrogen, methane, ethane. propane, butanes, pentane and ethylene, theyields of propylene, butylenes and amylenes pass through pronouncedmaxima as the depth of cracking is increased, and that these maximumyields in each case correspond to' a depth of cracking between about 60%and '70% when operating at temperatures above 1000 F. When operating at'750 F., on the other hand, these maxima are barely noticeable andfurthermore correspond to a depth of cracking of about 45%. Thus, bycontrolling and limiting the depth of cracking maximum yields of thesevaluable products may be obtained. Although the yields of ethylene donot go through such a maximum, the yields of ethylene are also muchgreater than those obtained by conventional high temperature operation.Also, although the yields of undesired gases such as methane and ethaneare higher than those obtained in the conventional cracking processes,they are lower than could be obtained without limiting the depth ofcracking to the specied limits.

The depth of cracking is controlled and retained below about andpreferably between 60% and 70%, by employing very high space velocitiesand by employing a mixed catalyst consisting of the adsorptive crackingcatalyst having a high activity and a substantially non-catalytic,non-adsorptive and non-combustible mineral diluent, These two controlsare interdependent. The space velocity, measured in terms of the tons ofhydrocarbon oil feed charged per hour per ton of the catalyst 1n thereactor, and designated weight hourly space velocity is preferably above6 and usually between about 6 and 10. Based on 4the more activecomponent of the catalyst mixsacarse eral ldiluent which hassubstantially no inner surface and is therefore substantiallynon-adsorptive. When such a catalyst mixture is used substantially allof the cokeis formed on and by the active catalyst component and verylittle if anyv is formed on or by the inert component.`

Thus, although the rate of coke formation with respect to the activecatalyst' remains the same,v

the concentration of coke in the mixed catalyst is reduced. By adjustingthe relative proportions of theA two catalyst components the depth vofcracking can be controlled and maintained within the desired limits.Also by suitable adjustment of the space velocity the relativeproportions of the two catalyst components may be such that theregeneration may be carried out with undiluted air with little or nocooling. Suitable non-combustible, non-adsorptive inert materials whichcan be used in the process of the invention are, for example, alphaalumina, sand, powdered quartz, powdered silicon, siliceous tailingsfrom ore dressing processes, powdered pumice, ground slag (provided thatit does not catalyzecarbon formation) ground magnesite,-ground dolomite,and the like. Also certain materials like bentonite and diatomaceousearth can be used since under the high temperature conditions prevailingthey quickly lose any activity that they might initially have. Thesevarious materials are pref'- erably used in the form of particles ofabout the same size range as the catalyst. For instance, in

are commonly used in catalytic cracking. It is forced by pump 2 throughcoil 3 of a suitable heater l. The preheated oilleaving the preheatervia line 5 picks up a regulated amount of hot freshly regeneratedcatalyst entering via standpipe t. The catalyst consists, for example.oi a substantially completely regenerated mixture of 60% syntheticsilica-alumina-zirconia cracking catalyst having a surface area of about150 square meters per gramand 40% of powdered silica. The powderedcatalyst, at a temperature of about 1250 F., is dispersed with-airentering via line l so that the resulting mixture is about by volume ofcatalyst. The amount of catalyst introduced is, for example, about 15parts by weight per part of oil, The preheated oil, upon contacting thecatalyst is immediately heated ,to about 1150 F. Part of the heat comesfrom the catalyst and part of it cornes from the combustion of about0.5% ci the oil feed. The mixture of oil and catalyst passes via line 5into bottom draw-oi reactor 8 wherein the oil vapors areV contacted withuidized catalyst at an effective tion of naphtha and gaseous productsmay be fluid catalyst crackingthe inert material may suitably be apowder passing a 100 mesh sieve.

It will be appreciated that the catalytic cracking according to thepresent invention is carried out attemperatures much above thosenecessary for thermal cracking. Most oils to`be cracked begin to undergothermal cracking at temperatures in the neighborhood of 700825 11A/Ifany appreciable amount of thermal cracking is, however, allowed to takeplace the yieldand quality oi the products are considerably reduced. Inorder to prevent any substantial thermal cracking from taking place theoil to be cracked is preheated toincipient cracking temperatures onlyand then the preheated oil is rapidly heated to the desired crackingtemperature in the presence of the cracking catalyst. This is eil'ected.either entirely by the catalyst or by the catalyst and a partialcombustion in the presence ,of the catalyst. Thus the desired crackingtemperatures may be reached almost instantaneously upon introducing thehot regenerated catalyst into theoil. In a preferred modification oi theprocess of the invention, however,` the hot regenerated catalyst ismixed with air and this mixture is in-` troduced into the preheated oil,In a; typical case the hot regenerated catalyst withdrawn from theregenerator is mixed with air to form a `miirture having about 80% byvolume of air and this mixture is introduced into the preheated oil; the

taken oi overhead to a condenser IIAand separator I2. Gaseous productsmay be removed from the separator via line I3 and treated in anyconventional manner. A part of the liquid conden sate may be recycledvia line Il to serve as reflux and the remainder may be withdrawnvialine I5. Light gas oil may be removedvia line I6, and

heavy gas oil may be removed via line I'I, A

heavy oil may be removed via line I8. These various higher boilingproducts may be recycled to the catalytic cracking step or treatedorutilized in any of the conventional manners,

Partially spent catalyst is continuously withdrawn from reactor 8 viastandpipe I9. This partially spent catalyst is picked up by a stream ofpartially spent regeneration gas and carried via line 20 to a lowtemperature regenerator 2l. The temperature in regenerator il is forexample. between about 1000 F. and 1100 F.: the residence time of thecatalyst therein is suillcient to remove only a portion of thecarbonaceous deposits. The partially regeneratel catalyst iscontinuously withdrawn via standpipe 22. This catalyst is picked up bygastream of undiluted air forced in by blower 23 and is carried via line24 to a high temperature regenerator 26. The regenerationin regenerator25 is carried out at a temperature of about 1250 F. and the residencetime of the catalyst therein is sufficient to insure 4is continuouslywithdrawn via standpipe 8 as deair burns between about 0.25% and 1%' ofthe l I oil feed and the liberated heat is utilized in raising thetemperature of the oil vapors,

Certain' aspects of the invention may best described in connection withan operation comi prised within its scope.V To aid in'this descriptionreference is had to the attached drawing wherein there is shown bymeansof diagrammatic figures not drawn to scale some of the apparatuscracked enters via line I. 'I'he feed may be a naphtha, gas oil. reducedcrude, or in fact any of the oils boiling above 155 C. (311 P.) such asand flows of a modified iluid catalyst cracking plant. Referring to thedrawing, the oil to be scribed.` YThe partially spent regeneration gasor a portion thereof may be cycled via line 20 to the low temperatureregenerator 2|. Additional air may be supplied to the lowtemperatureregenerator via line 26. As pointed out. part of the air is passed via,line 1 to regenerated catalyst in lstandpipe 8. In thisvtwo-temperature method of catalyst regeneration much highertemperatures may be employed in the second, or high temperavture stepwithout damaging the catalyst.

We claim as our invention:

1. Aprocess for the catalytic cracking of hydrocarbon oils boiling aboveabout 311911'. which comprises preheating the oil to be cracked toanincipient cracking temperature between about '700 F'. and 825 F.,combining the preheated oil with a mixture of air and a hot regeneratedcatalyst consisting of a iinely divided adsorptivesilicaalumina-zirconiacomposite cracking catalyst diluted with such anamount of a finely divided substantially non-adsorptive andnon-combustible mineral diluent as to aord a depth of cracking between60 and 7 0%, said catalyst being at a temperature at least 90 F. abovethe cracking temperature and the amount of said air-catalyst mixcrackingtemperature in the range of 1200 F.- 1400 F., retaining said oil incontact with said catalyst at said cracking temperature for a period oftime corresponding to a. weight hourly space velocity between about 6and l0, separating cracked products rich in normally gaseous olens fromthe catalyst, partially regenerating the cata-V lyst and then completingthe regeneration of the catalyst in a separate step by burning with airat a temperature between l200 F. and 1400 F. without cooling. v

2. A process for the catalytic cracking of hydrocarbon cils boilingabove about 311 F. which comprises preheating the oil to be cracked toan incipient cracking temperature between about '700 F. and 825combining the preheated oil with a mixture of air and a hot regeneratedcatalyst consisting of s, nely divided adsorptive cracking catalystdiluted with such an amount of a finely divided substantiallynon-adsorptive and non-combustible mineral diluent as to aiord a depthof cracking between 60 and 70%, said catalyst being at a temperature atleast 90 F. above the cracking temperature and the amount of saidair-catalyst mixture being adjusted to heat the preheated oil to acracking temperature in the range of l200 F.l400 F., retaining said oilin contact with said catalyst at said cracking temperature for a periodof time corresponding to a weight hourly space velocity between about 6and 10,'separating cracked products rich in normally gaseous olelns fromthe catalyst, partially regenerating the catalyst and then completingthe regeneration of the catalyst in a. separate step by burning with airat a temperature between l200 F. and 1400 F. without cooling.

3. A process for the catalytic cracking of hydrocarbon oils Aboilingabove about 311 Fgwhich comprises preheating the oil to be cracked to anincipient cracking temperature between about '700 F. and 825 F.,combining the preheated oil with a mixture of air and a hot regeneratedcatalyst consisting of a nely divided adsorptive silicaalumina-zirconiacomposite'cracking catalyst dilluted with such an amount oi a finelydivided substantially non-adsorptive and non-combustible mineral diluentas to afford a depth of cracking ture being adjusted to heat thepreheated oil to a secarse -between and '70%. said catalyst being at a.temperature at least F. above the cracking temperature and the amount ofsaid air-catalyst mixture being adjusted to heat the preheated oil to acracking temperature above about 1022 F., retainingsaid oil in contactwith said catalyst at said cracking temperature for a period of timecorresponding to a weight hourly space velocity of at least 6,separating cracked products rich in normally gaseous olefins from thecatalyst, and regenerating the catalyst in a separate step by burningwith air without cooling.

4. A process for the catalytic cracking of hydrocarbon oils boilingabove about 311 F. which comprises preheating the oil to be cracked toan incipient cracking temperature between about 700 F. and 825 F.,combining the preheated oil with a mixture of air and a hot regeneratedcatalyst consisting of a nely divided adsorptive cracking catalystdiluted with such an amount of a nely divided substantiallynon-adsorptive and non-combustible mineral diluent as to ailord a depthof cracking between 60% and 70%, said catalyst being at a temperature atleast 90 F. above the cracking temperature and the amount of saidair-catalyst mixture `being adjusted to heat the preheated oil to acracking temperature above about 1022 F., retaining said oil in contactwith said catalyst at said cracking temperature for a period of timecorresponding to a weight hourly space velocity of .at least 6,separating cracked products rich in normally gaseous oleins from thecatalyst and regenerating the catalyst in a separate step by burningwith air without cooling.

5. A process for the catalytic cracking of hydrocarbon oils boilingabove about 311 F, which comprises preheating the oil to be cracked toan incipient cracking temperature between about 700 F. and 825 F.,combining the preheated oil with a mixture of air and a hot regeneratedcatalyst consisting of a finely divided adsorptive cracking catalystdiluted with such an amount of a finely divided substantiallynon-adsorptive and non-combustible mineral diluent as to afford a depthof cracking between 60% and '70%, said catalyst being at a temperatureat least 90 F. above the cracking temperature and the amount of saidair-catalyst mixture being adjusted to heat the preheated oil to acracking temperature above about 1022 F., retaining said oil in Contactwith said catalyst at said crackingtemperature for a period of timecorresponding to a weight hourly space velocity of at least 6,separating cracked products rich in normally gaseousl olefns from thecatalyst and regenerating the catalyst in a separate step by burningwith air at a temperature between 1200 F. and 1400 F.

BERNARD S. GREENSFELDER.

STANLEY Z. PERRY.

